The invention is concerned with apparatus for and a method of producing a continuous stream of a particulate material and where two or more particulate constituents are supplied producing a continuous stream of a mixture of the constituents. The invention is particularly, but not exclusively, concerned with the production of a continuous stream of cement-, gypsum- or plaster-based mix either dry or as a slurry containing liquid (e.g., water). In such mixes, a cement, gypsum or plaster powder is usually reinforced by further particulate constituents such as crushed rock or stone, gravel, sand or manufactured aggregate. It is also known to add a fibrous reinforcing material such as glass fibre, asbestos or plastics or metal filaments to the mix. It is important that the reinforcing materials shall be thoroughly mixed with the powder base and, where a slurry is to be produced, with the correct quantity of water to obtain proper hydration of the cement or other powdered base material.
The quantity of water used in relation to the quantity of cement has a major influence on the workability of the cement mortar or concrete produced and on its final strength. In conventional cement-mixing processes water/cement ratios by weight of between 35 and 100% are commonly employed, whereas a ratio by weight of 28% water/cement is sufficient to obtain hydration; but in practice this is unlikely to be obtained.
In conventional cement-mixing processes, the cement and various reinforcing materials, such as sand and aggregate, are measured by volume or weight and mixed together in batches. In a continuous process plant such as that employed in our co-pending U.S. patent application No. 609,498 it is desirable to use a continuous mixing process providing a continuous stream of mixture. This is particularly important where fibrous reinforcing material, such as glass fibre, is to be incorporated in the mix, as the fibres should undergo a minimum amount of disturbance to avoid damage to or degradation of the fibre and the consequent risk of corrosion by the cement and loss of strength in the final material.